39mm FCR on XR400 ?
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snaggleXR4
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- Aug 5, 2001
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Hey,
I didn't try the FCR, but I did have the Mikuni on my XR4. It worked really well. However, the best mod I made to my '96 XR400 was selling it and buying a '00 XR650R. Sure, the Big Red Pig is heavy when you try to pick it up, but when riding, it feels absolutely no heavier than the XR400. The only reason the 650R sucks as a woods bike is beacause of the TALL gearing, slap on a 13T front sprocket or a 14/52 combo and you have a monster that will idle over logs and up hills, and still do 90mph+. The handling and overall balance of the bike puts the XR400 to shame. From long whooped out dirt roads to roots the suspension takes it all with little complaint. The power is phenomenal. The Pig will yank your arms off and permanently burn a smile to your face.
Sorry about getting off on a tangent. The point is, you can spend all the money in the world on a bike to improve it, but in the end it is still the same. Furthermore, learn to properly jet your stock carb. Then go spend $400+ on a FCR or Mikuni or Edelbrock. Then you will see that you must learn to jet the new carb now and/or it's not $400 better than the properly tuned stock carb. Again, on my 650R, I've got the stock carb working as well as the Mikuni was on my 400. Throttle response is nearly instantaneous, accelleration is smooth and clean, and the bike starts easy cold and hot. You can make your stock carb work that way if you put in the time. I say save your money for handlebars and/or other goodies, or for a 650R, you would NEVER regret it. Good luck.
I didn't try the FCR, but I did have the Mikuni on my XR4. It worked really well. However, the best mod I made to my '96 XR400 was selling it and buying a '00 XR650R. Sure, the Big Red Pig is heavy when you try to pick it up, but when riding, it feels absolutely no heavier than the XR400. The only reason the 650R sucks as a woods bike is beacause of the TALL gearing, slap on a 13T front sprocket or a 14/52 combo and you have a monster that will idle over logs and up hills, and still do 90mph+. The handling and overall balance of the bike puts the XR400 to shame. From long whooped out dirt roads to roots the suspension takes it all with little complaint. The power is phenomenal. The Pig will yank your arms off and permanently burn a smile to your face.
Sorry about getting off on a tangent. The point is, you can spend all the money in the world on a bike to improve it, but in the end it is still the same. Furthermore, learn to properly jet your stock carb. Then go spend $400+ on a FCR or Mikuni or Edelbrock. Then you will see that you must learn to jet the new carb now and/or it's not $400 better than the properly tuned stock carb. Again, on my 650R, I've got the stock carb working as well as the Mikuni was on my 400. Throttle response is nearly instantaneous, accelleration is smooth and clean, and the bike starts easy cold and hot. You can make your stock carb work that way if you put in the time. I say save your money for handlebars and/or other goodies, or for a 650R, you would NEVER regret it. Good luck.
ochster
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TR, While having no experience with the 39mm FCR, I have heard it lacks the low end crispness of the smaller pumpers. This would make sense to me, as I have experienced the same carb symptoms when using 36mm carbs on the 300's. My take is the intake velocity is slower, creating more difficulty in jetting. Obviously the more open your riding is, other mods, and the amount work to the head, could make this a mute point.
snaggle, I'm surprised at you! I was amped up to shoot your response full of holes, but decided I didn't have the time.
snaggle, I'm surprised at you! I was amped up to shoot your response full of holes, but decided I didn't have the time.
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Thanks Ochster, I have both the 36mm Mikuni and the 35FCR. I was ordering some new jet needles the other day, when carby sales man was telling that a new 39mm FCR kit has been made for the XR400. The spigots measure 47mm OD. It will be a tight fit. I agree that the carby is probably too big. Similar problem to the KTM400 (?).
My Xr400 still runs the mikuni. I now run pilot of 20 and main of 125. When I went big on the pilot I was amazed how sensitive the fuel screw became. Previously beyond two turns out there was not real affect. The 36mm Mikuni would be the most underated carby around. It is everything the FCR should be. Adjustable acceleratpr pump, actuation and duration. No need for BK or P38 or what ever other "fixes" are available. No need to have a hot start switch. It has an upright design and its cheaper. Big bore riders should be looking at the Mikuni HSR series instead of the FCR.
I was just curious if any DRNer had used the 39mm.
My Xr400 still runs the mikuni. I now run pilot of 20 and main of 125. When I went big on the pilot I was amazed how sensitive the fuel screw became. Previously beyond two turns out there was not real affect. The 36mm Mikuni would be the most underated carby around. It is everything the FCR should be. Adjustable acceleratpr pump, actuation and duration. No need for BK or P38 or what ever other "fixes" are available. No need to have a hot start switch. It has an upright design and its cheaper. Big bore riders should be looking at the Mikuni HSR series instead of the FCR.
I was just curious if any DRNer had used the 39mm.
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snaggleXR4
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- Aug 5, 2001
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Ochster,
Why are you surprised at me? Yes, for a long time I swore by my XR400, and I was very happy with the Mikuni pumper on my bike. However, in retrospect, compared to my rejetted stock carb, I didn't gain THAT much spending $369 for the Mikuni. I did gain a tad better throttle response, easier starting and smoother acceleration, but only a small percentage better. Now, due to the added experienced I gained by rejetting and adjusting the needle on my 650R, I believe I could have made the stock XR4 carb run even closer to the Mikuni.
Finally, about the rant on the 650R. After realizing how much better the 650R handles, not to mention the power, I could have put $3000 into the 400 and still not have near the bike. Now, I really hate to sound like all the people who say that any bike other than theirs is a worthless piece, but I'm just thoroughly impressed with my 650R.
Keep up the good work Ochster, you are THE man. I'll be needing your expertise here soon when I get into some heavy duty preventative maintenance on my new bike. Good luck.
Why are you surprised at me? Yes, for a long time I swore by my XR400, and I was very happy with the Mikuni pumper on my bike. However, in retrospect, compared to my rejetted stock carb, I didn't gain THAT much spending $369 for the Mikuni. I did gain a tad better throttle response, easier starting and smoother acceleration, but only a small percentage better. Now, due to the added experienced I gained by rejetting and adjusting the needle on my 650R, I believe I could have made the stock XR4 carb run even closer to the Mikuni.
Finally, about the rant on the 650R. After realizing how much better the 650R handles, not to mention the power, I could have put $3000 into the 400 and still not have near the bike. Now, I really hate to sound like all the people who say that any bike other than theirs is a worthless piece, but I'm just thoroughly impressed with my 650R.
Keep up the good work Ochster, you are THE man. I'll be needing your expertise here soon when I get into some heavy duty preventative maintenance on my new bike. Good luck.
Back about 11 years ago, I built an '85 XR350 (baby 400) with a mild cam, some porting and a pipe to work it out. Put on a 36 Mik. to start because that was what WB was recommending at the time. I talked the owner into putting a 40mm (bored 38) flat slide on it and it worked GREAT. Pulled hard all through the powerband and was a great bike.. 39 too big for the 400? Not likely. Won't hurt to clean up the porting and put a good pipe on it to help out.
Swiss
Swiss
ochster
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TR,
I have also had better luck running a larger pilot (17.5) on the opened up XR4's. Are you running the EBY series needles?
Snaggle,
While I will agree, for the average guy that the stock carb can be jetted and set-up to run decent, I believe the Mikuni to be a good investment. It has been my experience, that many XR owners just get frustrated with the starting drill, and are willing to pay the dough. Considering most people spend more than that on a exhaust system, in comparison I think the pumper is a better value, and performance option.
Having been around both the XR4 and 650R, they are like night and day in thier differences and intended purpose/audience. In the tight nasty terrain that the XR4 excels at, the 650R is a big machine, that is mercilleslly boiling over. I often do not even see a single 650R at Enduro style events, yet there will be dozens of XR4's. The simplicity of the XR4 has proven to be one of it biggest attractions, and a class leader in holding it's resale value. I would expect the tables to be turned in the faster more open style desert races, wich only shows just how different these two machines really are.
I'm convinced, that the average middle aged enthusiest, enjoy's modding and tinkering with his bike, as much as he does riding it. You and I both agree, it does not change what it is. But what it does, is personally tailor his/her machine to it's intended rider, and duties. Not to mention the amount of personal satisfaction, and positive constructive use of time and mental energy, that otherwise may be directed in a less than positve direction/manner. You obviously found this in your new scoot-cool!
Let me say "Thank You" for your vote of confidence. But I openly admit, I have been humbled and schooled here many times, it's what keeps me coming back.
I have also had better luck running a larger pilot (17.5) on the opened up XR4's. Are you running the EBY series needles?
Snaggle,
While I will agree, for the average guy that the stock carb can be jetted and set-up to run decent, I believe the Mikuni to be a good investment. It has been my experience, that many XR owners just get frustrated with the starting drill, and are willing to pay the dough. Considering most people spend more than that on a exhaust system, in comparison I think the pumper is a better value, and performance option.
Having been around both the XR4 and 650R, they are like night and day in thier differences and intended purpose/audience. In the tight nasty terrain that the XR4 excels at, the 650R is a big machine, that is mercilleslly boiling over. I often do not even see a single 650R at Enduro style events, yet there will be dozens of XR4's. The simplicity of the XR4 has proven to be one of it biggest attractions, and a class leader in holding it's resale value. I would expect the tables to be turned in the faster more open style desert races, wich only shows just how different these two machines really are.
I'm convinced, that the average middle aged enthusiest, enjoy's modding and tinkering with his bike, as much as he does riding it. You and I both agree, it does not change what it is. But what it does, is personally tailor his/her machine to it's intended rider, and duties. Not to mention the amount of personal satisfaction, and positive constructive use of time and mental energy, that otherwise may be directed in a less than positve direction/manner. You obviously found this in your new scoot-cool!
Let me say "Thank You" for your vote of confidence. But I openly admit, I have been humbled and schooled here many times, it's what keeps me coming back.
snaggleXR4
Member
- Aug 5, 2001
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Ochster,
Again, you make a good point. I do love to tinker with my bikes almost as much as I love riding them. That includes modifying the bike with better carbs, pipes etc. In the past, I've always bought an XR's Only pipe, and they sent me the jets they thought I needed. I would install them and be happy. I understood the air/fuel mixture theory of carbs, but didn't know how to read the signs of a mis adjusted carb. With the 650R, it already had a WB E-series pipe, and the guy had changed the main jet only. When I went to test ride the bike, the guy had the carb so messed up. It would bog on midrange and the idle was whacked. After pulling the carb out of the bike 5+ times and making different adjustments, I finally got the carb running great. Better than I thought any XR carb could. I did knock the Mikuni in my first post, I shouldn't have it was a good carb. In retrospect, it would have been much better if I knew then what I know now. At this point, I would not even think about buying a different carb for the 650R unless the stock one breaks. I plan to put the $ towards a dual sport kit.
Again, you make a good point. I do love to tinker with my bikes almost as much as I love riding them. That includes modifying the bike with better carbs, pipes etc. In the past, I've always bought an XR's Only pipe, and they sent me the jets they thought I needed. I would install them and be happy. I understood the air/fuel mixture theory of carbs, but didn't know how to read the signs of a mis adjusted carb. With the 650R, it already had a WB E-series pipe, and the guy had changed the main jet only. When I went to test ride the bike, the guy had the carb so messed up. It would bog on midrange and the idle was whacked. After pulling the carb out of the bike 5+ times and making different adjustments, I finally got the carb running great. Better than I thought any XR carb could. I did knock the Mikuni in my first post, I shouldn't have it was a good carb. In retrospect, it would have been much better if I knew then what I know now. At this point, I would not even think about buying a different carb for the 650R unless the stock one breaks. I plan to put the $ towards a dual sport kit.
ochster
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IMHO, there is no problem making the oem 30mm Keihin perform decent with just a typical 77 or 78mm 10:5 to 11:1 piston. I also believe this to be the most durable, best bang for money-less headaches mod you can do to these bikes. When building engines with different cams and compression, I have fitted 36mm Mik pumpers, with nice performance gains. I am now in the process of building a engine that will be set up with a 35mm FCR, I havn't yet put one a 250/280. When taking this mod on, one needs to be aware it will involve a susbstantial amount of patience and mechanical skills. Everything from throttle assy's, airbox modifications, jetting, cable routing, etc, will need to be fitted and ironed out. IMHO, if you are not up for this, you are best to save your money for other things. Jetting specs are commonly available for the average/normal piston kit's with the oem carb., and is still very user friendly. I know there are lot's of "flat slide-non pumper" carbs in use. But if I'm going to go through the energy of fitment and jetting, etc., I prefer the pumper.
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xrsforever
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- Nov 2, 2000
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IMHO,I have tried various carbs on the little XR280, and for my style of riding the Mikuni Flatside 34MM seems to work the best. I also use a CR throttle assembly, and a XR400 air boot for the carb.:cool:
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xrsforever
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- Nov 2, 2000
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No I have not tried the FCR on the 280,I have on an olderXR 400 with mixed results. It seemed on the 400 I sacrificed low end for big gains in the mid and top.
ochster
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There are many sources for piston kits, I usually use XR's Only, and I like the 78mm JE. They advertise it's 11:1, but they are actually 10.5:1 in my experience. I highly advise to spend the extra money and have a oversize cylinder sleeve installed, of wich the same outfit can help you. Otherwise there is very little meat left on the cylinder walls, and it will wear rapidly. For a basic no-frills woods machine, I like your ingredient list. I alway's use a quality race fuel, but know lots of people running this package on pump stuff. A large part of that equation will be how hard (hot) you run/ride the machine. I typically use a UNI filter with the high flow cage, and am partial to the White Bros. E-series muffler or XR's Only megaphone. They have a new quiet turned down tip that is suppose to work decent with there megaphone, as the supertrapp can be a little noisy.
Scott in KC
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Caught this thread a little late, but I just got done helping a buddy put his 400ex quad back together with the following...GT Thunder race porting, JE 10.5:1 piston, GT cam, 39mm FCR. Needless to say it's not even in the XR400 class anymore let alone the 400 ex class...it hauls the wood! Having been all through the jetting on my WR426 I was able to get his jetting dialed in pretty good. Now this motor is very modified and it took the "thump" out of the motor. It want's a higher idle and want's to be run on the needle. I mean, it still punches hard right off the bottom better than stock, but REALLY pulls in the middle now. The carb works very well with this setup, but not sure if I would spend the dough if that were the only mod. My biggest complaint with that full race slant FCR is there is no choke and no tab to do the "BK" mod which shortens the accelerator pump duration. Stock it pumps WAY too long (like 2 full seconds) and needs to be shaved down a bit (like 1/2 sec.) IMO, just like the YZ's & WR's. You can change the timing of it, but I haven't figured out a (reasonable) way to cut the pump time down. I'm not a quad guy at all, but I was very impressed with how this engine runs. It makes power all the way to the 9500 rpm redline!
ochster
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Bonzo,
My advice would be to utilize the stock cam, as long as it and the rockers were in good shape. I believe it to be very nice in your implied usage. It also is easiest on other parts, that otherwise become weak links and will need to be upgraded. Longevity and maintenance will suffer as well. It is also my experience the oem carb becomes a hindrance when going to more rev oriented cams along with added compression. A little bump in compression and displacement is a wonderful thing in these motors.
My advice would be to utilize the stock cam, as long as it and the rockers were in good shape. I believe it to be very nice in your implied usage. It also is easiest on other parts, that otherwise become weak links and will need to be upgraded. Longevity and maintenance will suffer as well. It is also my experience the oem carb becomes a hindrance when going to more rev oriented cams along with added compression. A little bump in compression and displacement is a wonderful thing in these motors.